Leoch AGM VRLA batteries indicate Valve Regulated Lead Acid Batteries with the following features: Maintenance-free, no water adding required; sealed valve-regulated, spill proof and leak proof; using unilateralism exhaust (safe vent valve) design on the battery cover, when the battery internal pressure have been up to the specifically value, the safe vent valve will open automatically, and will close after the pressure has been discharged, which can prevent the air to enter into battery.